1. Field of the Invention
The present invention relates to structural improvements on cut-off valves and means for detecting whether fuel tanks are filled up with fuels, cut-off valves and means which are disposed on automobile fuel tanks.
2. Description of the Related Art
In the vicinity of automobile fuel tanks, a vaporized-fuel circulating system, a so-called evaporator circuit, is disposed. The evaporator circuit leads vaporized fuels from fuel tanks to external canisters. The vaporized fuels are then adsorbed to activated carbon and the like, and are stored temporarily therein. Thus, the evaporator circuit inhibits the pressure increment within fuel tanks, pressure increment which results from the increment of vapor pressure. The canisters are connected with engines, and engines exert an inlet negative pressure to release the adsorbed vaporized fuels from activated carbon to mix them into an air-fuel mixture. Accordingly, the adsorbed vaporized fuels are used again as fuels.
The evaporator circuit is naturally provided with an opening, a so-called evaporator opening, which is formed in fuel tanks. The evaporator opening is generally formed at the uppermost portion of fuel tanks in order to inhibit liquid fuels from flowing into the evaporator circuit. However, when the level of liquid fuels move up and down, there might arise a fear that liquid fuels flow into the evaporator circuit through the evaporator opening. If liquid fuels flow even into the canister, they adsorb onto the activated carbon so that they might impair the usual vaporized fuel-adsorbing action of the activated carbon.
Hence, the evaporator opening has been conventionally provided with a variety of cut-off valves. As for the cut-off valves, floating valves have been often used as described later. When the level of liquid fuels rises abnormally, the floating valves float upward by buoyancy to close the evaporator opening. Consequently, the floating valves inhibit liquid fuels from flowing into the evaporator circuit.
Moreover, fuel tanks are provided with means for detecting whether fuel tanks are filled up with fuels when fuels are supplied. As for the means for detecting filled-up fuel tanks, apparatuses comprising a floating valve have been often used as described later. The floating valve closes an opening of fuel tanks to heighten the pressure within fuel tanks. Thus, fuel supply guns are turned off automatically.
For example, Japanese Unexamined Patent Publication (KOKAI) No. 11-229,984 discloses an apparatus for inhibiting fuels from flowing out. The flow-out fuel inhibitor apparatus is provided with a shut-off valve and a cut-off valve. The shut-off valve lets a gas, which includes a fuel vapor generating in a large volume, flow to a canister when a fuel is supplied. The cut-off valve lets a gas, which includes a fuel vapor, flow to a canister when a fuel is not supplied.
The apparatus is disposed at the top in a fuel tank, and comprises an upper housing 100 and a lower housing 200 as illustrated in FIG. 3. The upper housing 100 is communicated with a not-shown canister. Moreover, the upper housing 100 and the lower housing 200 are communicated with each other by a minor-diameter first communication passage 101 and a major-diameter second communication passages 102.
A first float 201 and a second float 202 are disposed in the lower housing 200. The first float 201 is disposed in a cylinder-shaped first space 201a. The second float 202 is disposed in an annular second space 202a which is formed separately around the first space 201a. The second float 202 is formed as a cylinder shape.
The first float 201 and the second float 202 have a valve body 201b and a valve body 202b, respectively, at the top. The valve body 201b and the valve body 202b close the first communication passage 101 and the second communication passage 102, respectively, by the up-and-down movements of a level of liquid fuels. The first float 201 and the second float 202 are urged upward by a spring 203 and a spring 204, respectively. However, the valve body 201b or the valve body 202b keeps the first communication passage 101 or the second communication 102 open until liquid fuels float the first float 201 or the second float 202 upward.
Further, a minor hole 205 is formed at the top of the lower housing 200. The first space 201a is communicated with the vapor phase of fuel tanks by way of the minor hole 205. Furthermore, communication holes 206 are formed at the bottom of the first space 201a and the second space 202a. The first space 201a and the second space 202a are communicated with the inside of fuel tanks by way of the communication holes 206. Moreover, a central cylinder 207 and an annular cylinder 208 are formed in the lower housing 200. The central cylinder 207 extends downward under the first space 201a, and opens at the bottom end. The annular cylinder 208 is formed around the central cylinder 207, extends downward under the second space 202a, and opens at the bottom end.
The apparatus operates in the following manner. When fuels are supplied and the level of liquid fuels are at a position 300 disposed downward below the bottom end of the lower housing 200, vaporized fuels flow into the first space 201a and second space 202a by way of the communication holes 206, and flow into a canister through the upper housing 100 by way of the first communication passage 101 and second communication passage 102. Moreover, some of the vaporized fuels flow into the first space 201a by way of the minor hole 205, and flow into the canister through the upper housing 100 by way of the first communication passage 101. Thus, fuels are supplied smoothly without increasing the pressure within fuel tanks.
Moreover, after the level of liquid fuels reaches a position 301 disposed at the bottom end of the lower housing 200, the level of liquid fuels rises only in the annular cylinder 208, and liquid fuels flow into the second space 202a through the communication holes 206 to float the second float 202 upward, because the gaseous pressure in the central cylinder 207 is higher than the gaseous pressure within fuel tanks. When the second float 202 floats upward and the valve body 202b closes the second communication passage 102, the gaseous pressure within fuel tanks increases sharply, the automatic turning-off mechanism of fuel supply guns is actuated to stop supplying fuels. Thus, it is possible to detect whether fuel tanks are filled up with liquid fuels.
In addition, when the level of liquid fuels waves in driving, liquid fuels are inhibited from flowing into the upper housing 100, because the second float 202 floats upward to close the second communication passage 102 in the first place. Moreover, when the level of liquid fuels waves more violently, liquid fuels are further inhibited from flowing into the upper housing 100, because the first float 201 floats upward as well to close the first communication passage 101.
However, the above-described conventional apparatus is provided with the two float valves and two communication passages, respectively. Accordingly, the conventional apparatus suffers from a problem that it is difficult to design so as to operate each of them accurately. Moreover, the conventional apparatus is associated with the drawback of high cost, because it comprises a large number of component parts. In addition, there arises another problem that the disposition space is limited greatly, because it is required to enlarge the diameter of the second float 202 and the diameter of the second space 202a. 
Moreover, it is necessary to manufacture a great number of the lower housings 200 and second floats 202 whose shapes are changed variously when the conventional apparatus is applied to fuel tanks whose shape and capacity differ with each other. Thus, the conventional apparatus suffers from a drawback that the man-hour requirement for the manufacture goes up remarkably.
Hence, the assignee of the present invention proposed a flow-out fuel inhibitor apparatus, which is provided with one and only floating valve to demonstrate both functions, the detection of filled-up fuel tanks and the cut-off valve, in Japanese Patent Application No. 2001-364,172. In accordance with the flow-out fuel inhibitor apparatus, it is possible not only to make the construction compact and share the component parts but also to achieve the reduction of cost and man-hour requirement, because the one and only floating valve demonstrates the two functions, the detection of filled-up fuel tanks and the cut-off valve.
As illustrated in FIG. 4, the flow-out fuel inhibitor apparatus, an example set forth in the Japanese patent application, comprises a cover 400, a breather pipe 500, an upper case 600, a substantially box-shaped lower case 700, and one and only floating valve 800. The cover 400 is disposed outside a fuel tank 300 having a top opening 301, has a communication passage 401 communicating with a canister, and is welded to the periphery of the top opening 301 of the fuel tank 300 in an airtight manner. The breather pipe 500 is disposed inside the fuel tank 300, extends downward, and has a top-end opening whose periphery is welded to the cover 400 in an airtight manner. The upper case 600 is formed as an inverted bowl shape having a bottom at the top end, has a communication opening 601 in the bottom, the communication opening 601 communicating with the communication passage 401 of the cover 400, and a substantially cylinder-shaped wall extending downward and held to the breather pipe 500. The lower case 700 is fixed to the upper case 600. The floating valve 800 is accommodated in the lower case 700, floats on a liquid fuel, and moves up and down in accordance with the up-and-down movements of a level of the liquid fuel, whereby opening and closing the communication opening 601 of the upper case 600.
Moreover, an O-ring 501 is held between the upper case 600 and the breather pipe 500, because it is necessary to joint the upper case 600 with the breather pipe 500 in an airtight manner.
The flow-out fuel inhibitor apparatus is assembled in the following manner. First, the lower case 700 with the floating valve 800 accommodated therein is held by fitting into the upper case 600, and the O-ring 501 is disposed on the outer periphery of the upper case 600. The resulting sub-assembly is held by fitting into the breather pipe 500. Thereafter, the periphery of the top-end opening of the breather pipe 500 is fixed by welding to the cover 400 by means of a hot-plate welding method. The thus assembled flow-out fuel inhibitor apparatus is inserted into the top opening 301 of the fuel tank 300, beginning with the leading end of the breather pipe 500. Finally, the bottom end of the cover 400 is fixed by welding to the periphery of the top opening 301 of the fuel tank 300 to assemble the flow-out fuel inhibitor apparatus with the fuel tank 300.
However, when the flow-out fuel inhibitor apparatus is assembled while interposing the O-ring 501 between the upper case 600 and the breather pipe 500, it is not possible to say that the operation is easy. Actually, the man-hour requirement has gone up remarkably. Moreover, the O-ring 501 is swollen to certain extent by fuels. Accordingly, the O-ring 501 presses the breather pipe 500 outward diametrically when the expansion force is large. Therefore, the stress concentrates on the welded portion between the breather pipe 500 and the cover 400. Consequently, it is necessary to enhance the welding strength at the welded-portion. Because of this as well, the man-hour requirement has gone up sharply. Moreover, when the O-ring 501 contracts, there is another fear for a drawback that the sealing property might lower between the upper case 600 and the breather pipe 500.
Moreover, since the breather pipe 500 and the upper case 600 make a dual construction, the diameter of the breather pipe 500 is enlarged more than necessary. As a result, the flow-out fuel inhibitor apparatus might suffer from problems in view of the installation space and cost.